1. Field of the Invention
This invention relates to a system for supplying high purity chemicals to a semiconductor, fiber optic, or the like, component production line. More particularly, this invention relates to a system of the character described which allows the production line to operate continuously, and without interruption.
2. Brief Description of Prior Art
Production lines for the manufacture of semiconductors, fiber optics, and the like components, typically include systems for supplying high purity processing chemicals to diffusion furnaces, either directly or in carrier gases.
The processing chemicals are liquids which may be directly injected into the processing stations, or which may be carried to the processing stations in a carrier gas. Direct chemical injection may be from bulk supply tanks, or may be from smaller supply containers which will be periodically refilled by bulk supply tanks. When the chemicals are applied by means of carrier gases, the liquid chemicals will be contained in temperature-controlled ampules, called "bubblers". A stream of an inert carrier gas, such as nitrogen, helium, or the like, is injected into the bubbler ampules. The inert carrier gas bubbles upwardly through the liquid chemical in the bubbler ampule and creates a chemical-saturated carrier gas atmosphere in the ampule in the space above the supply of liquid chemical contained therein. The chemically saturated carrier gas is continuously drawn out of the bubbler and transferred into the component processing station, such as a diffusion furnace, as noted above.
The aforesaid processing lines utilize very high purity chemicals, such as 1,1,1-trichloroethane (TCA), and tetraethylorthosilicate (TEOS); and dopants such as phosphorous oxychloride (POCl.sub.3), trimethylborate, and trimethylphosphate. The processing lines depend on a continuous supply of the chemicals being delivered from the chemical source in order to operate properly and efficiently. If the supply of the processing chemicals is interrupted, the production line must be shut down, and the diffusion furnace must be placed in a "idle" mode. If the chemical ampules are depleted of processing chemicals, they must be removed from the production line and replaced with freshly filled ampules.
In order to avoid the necessity of removing a bubbler ampule from the production line, one or more bulk chemical supply containers have been incorporated into the production line. One bulk supply container is connected to the bubbler ampule and is operable to replenish the chemical as the latter is removed from the ampule. The replenishment is a periodic process wherein a production line controller periodically replenishes the amount of processing chemical contained in the ampule with chemical from the bulk supply container so that the chemical is intermittently replaced in the ampule. This bulk supply container is a fixed component of the production line and cannot be readily removed therefrom. When a single bulk supply container is used in the production line, it must be periodically refilled with processing chemicals. The line must be shut down while the bulk supply container is refilled. The line can be run for a longer time period due to the use of the bulk supply container, however, the line still must be periodically shut down when the bulk supply container is depleted.
When two bulk supply containers are used, one is a fixed container and the other is a replaceable mobile container. The ampule is replenished with chemicals from the fixed bulk container, and the fixed bulk container is refilled with chemicals from the replaceable, or shuttle, bulk container. The fixed bulk container is typically positioned on a scale or connected to a load cell so that the volume of chemical in the fixed bulk container is continuously monitored. Signals are transmitted to the system microprocessor controller which are indicative of the volume of chemical remaining in the fixed bulk container. Typically, when the fixed bulk container is seen to be 75% full, the controller activates a chemical transfer valve system which transfers chemical from the shuttle bulk container to the fixed bulk container, and when the fixed bulk container has been refilled, the controller deactivates the chemical transfer valve system. Thus, the fixed bulk supply container will be refilled several times before the shuttle supply container must be refilled. When the shuttle bulk supply container has been substantially emptied, the shuttle container is removed from the production line and is refilled at an off-site chemical supply repository, which is typically far removed from the processing plant. At the present time, there are several such chemical supply repositories in the United States.
The use of fixed and shuttle bulk chemical supply containers has proven to be functionally operative, but it would be desirable to be able to provide an alternative replenishment system for the chemical ampules; and even more desirable to provide a chemical replenishment system with a controller microprocessor which can operate the system in alternative chemical replenishment modes, one having a fixed and a replaceable bulk chemical supply containers, and the other having two replaceable bulk chemical supply containers.